Personal computer systems are well known in the art. Personal computer systems in general, and IBM personal computers in particular, have attained widespread use for providing computer power to many segments of today's modern society. These systems are designed primarily to give independent computer power to a single user and are inexpensively priced for purchase by individuals or small businesses. Personal computer (PC) can typically be defined as desktop, floor standing, or portable computers that includes a system unit having a single central processing unit (CPU) and associated volatile and non-volatile memory, including RAM and BIOS ROM.
One of the distinguishing characteristics of these systems is the use of a motherboard or system planar to electrically connect these components together and to provide for adapter or expansion cards to be added to the motherboard to perform any of a wide variety of functions. These functions may be options which a user may select at the time of ordering the computer and which are installed prior to the user installing the computer or they may be chosen by the user to add to his existing computer. Examples of the functions performed by adapter cards include additional video cards to provide enhanced video output to a system monitor, audio cards to provide for recordal, playback and editing of data relating to audio, communication cards such as a modem card or a Local Area Network (LAN) card to allow communication with other computers over a network or a fax card to allow fax transmissions to be sent and received. Additionally, such adapter cards may provide for more memory to be added to an existing computer than can be added to the motherboard. A system typically also includes a system monitor, a keyboard, one or more flexible diskette drives, a fixed disk storage drive (also known as a hard drive), a so-called mouse pointing device, and an optional printer.
Since personal computers first became popular in the early 1980's, most of these expansion cards were suitable for the so-called Industry Standard Architecture (ISA) type of computer bus. With the advent of more powerful computers having wider data bus widths and differing architectures and protocols an early enhancement to this bus called the Extended Industry Standard Architecture (EISA) was produced. Adapter cards for both of these types of bus consist of a printed circuit board with electronic components mounted on the circuit board, a number of contact strips provided along an edge of the circuit board which are intended to plug into a connector of the corresponding type (ISA or EISA) on the motherboard and a plate-shaped mounting bracket at one end of the circuit board to provide mechanical fixing of the card to the computer system and also to provide for the positioning of connectors to allow connections to external devices to be made. The printed circuit board has tracks to connect together the components as is well known in the art.
The connectors into which the adapter cards are inserted were located on the motherboard, with the cards being located perpendicular to the plane of the motherboard. This had the disadvantages that firstly the height of the enclosure in which the personal computer was contained could not be less than the height of the adapter cards plus some allowance for the motherboard and connector and secondly that the area of the motherboard was increased by the necessity to allow a considerable space for the connectors.
To overcome the first problem, a riser card is used in many systems today, in which the riser card has a number of contact strips provided along an edge of the card which are intended to plug into a connector on the motherboard. The riser card itself then has several connectors on it into which adapter cards are plugged in. The riser card is typically located perpendicular to the plane of the motherboard and the adapter cards are typically located perpendicular to the plane of the riser card, so that the adapter cards are located parallel to the plane of the motherboard. The height of the enclosure may now be reduced to be only that required for the motherboard itself and the thickness and spacing required to provide for as many adapter cards as it is desired to provide slots for on the riser card. In addition, since components may be placed on the motherboard underneath the adapter card location and since there is now only one connector on the motherboard for the riser card, the motherboard may itself be made smaller.
More recently, adapter cards have been available which have a so-called Peripheral Component Interconnect (PCI) bus. These have different contact arrangements and connectors and are not interchangeable with ISA or EISA adapter cards. On ISA and EISA cards, the components are mounted on the face of the card which is seen when the contacts along the edge are towards the user and the end plate carrying any external connectors is on the right hand side. On PCI cards, the components are mounted on the opposite side.
IBM Technical Disclosure Bulletin, Vol.38, No.3. March 1995, p.489 discloses a package that has two connectors attached to the same Input/Output Processor (IOP). The IOP has two connectors, one suitable for the PCI bus and one suitable for a MicroChannel (MC) bus. A card is plugged into either the PCI connector or to the MicroChannel connector. The IOP determines which connector is in use and configures the card accordingly.
IBM Technical Disclosure Bulletin, Vol.38, No.2. February 1995, pp.161-163 discloses a riser card having a first adapter slot which can be shared between either a MicroChannel adapter card and a PCI adapter card or between an ISA adapter card and a PCI adapter card. Three card slots are provided in total, but only the first may be shared.
Published European Patent Application EP-0-687-983-A1 discloses a riser card having a single card slot which has two connectors for that slot, one being an ISA connector and one being a PCI connector. Only a single card slot has the ability to accept an ISA adapter card or a PCI adapter card.
All of the above arrangements require the adjacent ISA connectors and the adjacent PCI connectors to have a spacing of around 1.00 inches (25.4 mm) in order to allow the connectors to be mounted in position. The cards themselves only require a 0.80 inch (20.3 mm) spacing to allow for the components on a card not to touch the opposite surface of an adjacent card. A disadvantage of the above arrangements is that the circuit board area which is used on the motherboard is larger for a given number of connectors as 1.00 inch (25.4 mm) spacing has to be allowed for. In an arrangement that uses a riser card, the height of the riser card has to be greater for a given number of connectors.